Well-established power distribution systems exist throughout most of the United States, and other countries, which provide power to customers via power lines. With some modification, the infrastructure of the existing power distribution systems can be used to provide data communication in addition to power delivery, thereby forming a power line communication system (PLCS). In other words, existing power lines, that already have been run to many homes and offices, can be used to carry data signals to and from the homes and offices. These data signals are communicated on and off the power lines at various points in the power line communication system, such as, for example, near homes, offices, Internet service providers, and the like.
While the concept may sound simple, there are many challenges to overcome in order to use power lines for data communication. Power lines are not designed to provide high speed data communications and are very susceptible to interference. Additionally, federal regulations limit the amount of radiated energy of a power line communication system, which therefore limits the strength of the data signal that can be injected onto power lines (especially overhead power lines).
Power distribution systems include numerous sections, which transmit power at different voltages. The transition from one section to another typically is accomplished with a transformer. The sections of the power distribution system that are connected to the customers premises typically are low voltage (LV) sections having a voltage between 100 volts(V) and 240V, depending on the system. In the United States, the LV section typically is about 120V. The sections of the power distribution system that provide the power to the LV sections are referred to as the medium voltage (MV) sections. The voltage of the MV section is in the range of 1,000V to 100,000V. The transition from the MV section to the LV section of the power distribution system typically is accomplished with a distribution transformer, which converts the higher voltage of the MV section to the lower voltage of the LV section.
Power system transformers are another obstacle to using power distribution lines for data communication. Transformers act as a low-pass filter, passing the low frequency signals (e.g., the 50 or 60 Hz) power signals and impeding the high frequency signals (e.g., frequencies typically used for data communication). As such, some power line communications systems face the challenge of communicating the data signals around, or through, the distribution transformers.
In contrast, conventional communication media, such as coaxial cables, Ethernet cables, fiber optic cables, and twisted pair, typically provide significantly better characteristics for communicating data than power lines. However, the cost of installing the conventional communications medium (i.e., non-power line communications medium) may be very significant and in some instances, prohibitive from a business perspective. In particular, a major cost of installing such media is the segment that extends from the common communication link, which typically is along the street, to each customer premises. This segment typically requires a dedicated cable for each customer premises.
In a power line distribution system, up to ten (and sometimes more) customer premises typically will receive power from one distribution transformer via their respective LV power lines. These LV power lines constitute infrastructure that is already in place. Thus, it would be advantageous for a communications system to make use of this existing infrastructure in order to save time and reduce costs of the installation.
Typically, the LV power lines extend from each customer premises to a distribution transformer and are all electrically connected to each other remote from the premises such as near the transformer. Thus, the LV power lines that electrically connect one customer premises to a distribution transformer are also electrically connected to the LV power lines connected to all the other customer premises receiving power from that distribution transformer. Consequently, a communications system employing the LV power lines must be able to tolerate the interference produced by many users. In addition, the communications system should provide bus arbitration and router functions for numerous customers who share a LV subnet (i.e., the LV power lines that are all electrically connected to the LV side of the transformer).
These and other advantages are provided by various embodiments of the present invention.